On Mon, Jun 20, 2016 at 11:10:57AM +0300, Mika Westerberg wrote: > On Fri, Jun 17, 2016 at 11:32:09PM +0200, Lukas Wunner wrote: > > On Fri, Jun 17, 2016 at 03:48:24PM -0500, Bjorn Helgaas wrote: > > > On Fri, Apr 29, 2016 at 11:51:59AM +0300, Mika Westerberg wrote: > > [snip] > > > > + > > > > + /* > > > > + * Prevent runtime PM if the port is advertising support for PCIe > > > > + * hotplug. Otherwise the BIOS hotplug SMI code might not be able > > > > + * to enumerate devices behind this port properly (the port is > > > > + * powered down preventing all config space accesses to the > > > > + * subordinate devices). We can't be sure for native PCIe hotplug > > > > + * either so prevent that as well. > > > > > > Can we wordsmith this comment a bit? I'm not sure what "BIOS hotplug > > > SMI code" even is or why it is relevant. And it seems x86-centric so > > > may not apply to other arches. > > > > The comment pertains to: > > https://bugzilla.kernel.org/show_bug.cgi?id=53811 > > > > It was discussed on April 12/13: > > https://patchwork.kernel.org/patch/8782801/ > > > > Executive summary: > > On non-Macs, Thunderbolt is driven by the firmware in System Management > > Mode, on hotplug the CPU receives a Sytem Management Interrupt (SMI) and > > jumps to SMM code. This doesn't work reliably if the hotplug port has > > been transitioned to D3hot, the SMM code tries to access config space > > of hotplugged devices (not possible if port is in D3hot) and is apparently > > too dumb to check if the port is in D3hot and wake it up. > > That's the best guess what happens on non-Macs. > > Bjorn, do you want me to update the comment to open up what SMI means > and maybe add better explanation? I withdraw my request. I guess it's probably not worth doing anything right now. It's just a little out of place because this is theoretically generic code, but the whole SMM thing is x86-specific. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
